1. Field of the Invention
The present invention relates to a non-volatile semiconductor memory device, and more particularly to a flash memory of which contents in a memory block can collectively be erased.
2. Description of the Background Art
Recently, a non-volatile semiconductor memory device, in particular a flash memory, has increasingly been mounted on a battery-driven, portable instrument, and a more efficient writing or erasing method has been demanded.
For example, Japanese Patent Laying-Open No. 11-191296 discloses a technique directed to a controlled method of writing hot electrons for a non-volatile memory cell, aiming at optimization of writing to a cell. In other words, particularly with regard to soft writing after programming and erasing, a cell substrate is biased to a negative voltage with respect to a source region, and a control gate region of the cell receives a ramp voltage having a selected, predetermined gradient satisfying a balance condition.
In order to realize a quick and smooth operation or a long-lasting operation of a portable terminal, a further efficient internal operation sequence in a flash memory such as a programming operation or an erasing operation should be attained.